The denomination “mobile telecommunications system” refers generally to any telecommunications system, which enables a wireless communication connection between a mobile station (MS) and the fixed parts of the system when the user of the mobile station is located within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN). The majority of mobile telecommunications systems in use at the time of the filing of this patent application belong to the second generation of such systems, a well-known example being the GSM system (Global System for Mobile telecommunications). However, the invention also applies to the next or third generation of mobile telecommunications systems, such as a system known as the UMTS (Universal Mobile Telecommunications System).
Multi-user radio communication systems must have well-defined procedures for allocating radio resources (time, frequency) to individual radio connections. In this patent application we will consider especially packet-switched radio connections in cellular radio systems where each cell comprises a base station, which is arranged to communicate with a multitude of mobile stations. As an example we will discuss the well-known GPRS system (General Packet Radio Service), the known resource allocation procedures of which are laid down in the technical specification number GSM 04.60 published by ETSI (European Telecommunications Standards Institute) [1].
Packet switched wireless networks, such as GPRS (General Packet Radio Service), are designed to provide data services, e.g. Internet services, cost-effectively. In GPRS the channels are not dedicated to one user continuously but are shared between multiple users. This facilitates efficient data multiplexing. However, different kinds of data services have different requirements for the data connection. For example, Internet real time services have gained popularity during the past few years; IP (Internet Protocol) telephony and different streaming applications are already common in the Internet. These services have different requirements for the data connection compared to, for example, transferring facsimiles or email messages. Therefore the connection for the data transfer is usually established according to the service requirements, such as the Quality of Service (QoS) requirement. However, the use of many kinds of services during the same session then requires the use of several connections or “temporary block flows”, each being dedicated to a certain type of service.
In order to better understand the problems of the prior art solutions and the idea of the present invention, the structure of a prior art digital cellular radio system is next described in short, and GPRS is then described in more detail by briefly describing some parts of said specification [1].
FIG. 1a shows a version of a prior known GSM cellular radio system. The terminals MS are connected to the radio access network RAN which includes the base stations and the base station controllers/radio network controllers RNC. The core network CN of a cellular radio system comprises mobile services switching centres (MSC) and related transmission systems. If the system supports GPRS services, the core network also comprises Serving GPRS Support Nodes (SGSN) and Gateway GPRS Support nodes (GGSN). According e.g. to the GSM phase 2+ specifications developed from GSM the core network may provide new services such as GPRS. The new types of radio access networks can co-operate with different types of fixed core networks CN and especially with the GPRS network of the GSM system.
FIG. 1b shows architecture of a general packet radio service (GPRS). The GPRS is a new service that is currently based on the GSM system but it is supposed to be generic in the future. GPRS is one of the objects of the standardisation work of the GSM phase 2+ and UMTS at the 3GPP (3rd Generation Partnership Project). The GPRS operational environment comprises one or more subnetwork service areas, which are interconnected by a GPRS backbone network. A subnetwork comprises a number of packet data service nodes (SN), which in this application will be referred to as serving GPRS support nodes (SGSN) 153, each of which is connected to the mobile telecommunications system (typically to a base station through an interworking unit) in such a way that it can provide a packet service for mobile data terminals 151 via several base stations 152, i.e. cells. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile data terminals 151. Different subnetworks are in turn connected to an external data network, e.g. to a Public Data Network (PDN) 155, via GPRS gateway support nodes GGSN 154. The GPRS service thus allows the provision of packet data transmission between mobile data terminals and external data networks when the appropriate parts of a mobile telecommunications system function as an access network.
In order to access the GPRS services, a mobile station shall first make its presence known to the network by performing a GPRS attachment. This operation establishes a logical link between the mobile station and the SGSN, and makes the mobile station available for SMS (Short Message Services) 158, 159, over GPRS, paging via SGSN, and notification of incoming GPRS data. More particularly, when the mobile station attaches to the GPRS network, i.e. in a GPRS attachment procedure, the SGSN creates a mobility management context (MM context). Also the authentication of the user is carried out by the SGSN in the GPRS attachment procedure. In order to send and receive GPRS data, the MS shall activate the packet data address, which is to be used, by requesting a PDP activation procedure (Packet Data Protocol). This operation makes the mobile station known in the corresponding GGSN, and interworking with external data networks can commence. More particularly, a PDP context is created in the mobile station and the GGSN and the SGSN. The packet data protocol context defines different data transmission parameters, such as the PDP type (e.g. X.25 or IP), the PDP address (e.g. X.121 address), the quality of service (QoS) and the NSAPI (Network Service Access Point Identifier). The MS activates the PDP context with a specific message, Activate PDP Context Request, in which it gives information on the TLLI, the PDP type, the PDP address, the required QoS and the NSAPI, and optionally the access point name (APN).
FIG. 1b also shows the following GSM functional blocks: Mobile Switching Center (MSC)/Visitor Location Register (VLR) 160, Home Location Register (HLR) 157 and Equipment Identity Register (EIR) 161. The GPRS system is usually also connected to other Public Land Mobile Networks (PLMN) 156.
Functions applying digital data transmission protocols are usually described as a stack according to the OSI (Open Systems Interface) model, where the tasks of the various layers of the stack, as well as data transmission between the layers, are exactly defined. In the GSM system phase 2+, which in this patent application is observed as an example of a digital wireless data transmission system, there are five operational layers defined.
Relations between the protocol layers are illustrated in FIG. 2. The lowest protocol layer between the mobile station MS and the base station subsystem is the layer 1 (L1) 200, 201, which corresponds to a physical radio connection. Above it, there is located an entity corresponding to the layers 2 and 3 of a regular OSI model, wherein the lowest layer is a radio link control/media access control (RLC/MAC) layer 202, 203; on top of it a PDCP layer 204, 205; and topmost a radio resource control (RRC) layer 206, 207. Between the base station subsystem GERAN BSS of the generic radio access network and an interworking unit/core network IWU/CN located in the core network, there is assumed to be applied a so-called Iu interface, where the layers corresponding to the above described layers from L1 to PDCP are the layers L1 and L2 of the OSI model (blocks 208 and 209 in the drawing), and the layer corresponding to the above described RRC layer is the layer L3 of the OSI model (blocks 210 and 211 in the drawing).
The mobile station MS must include a higher-level control protocol 212 and a protocol 213 for serving higher-level applications, of which the former communicates with the RRC layer 206 in order to realise control functions connected to data transmission connections, and the latter communicates directly with the PDCP layer 204 in order to transmit such data that directly serves the user (for instance digitally encoded speech). In a mobile station of the GSM system, the blocks 212 and 213 are included in the above-mentioned MM layer.
In GPRS, a Temporary Block Flow (TBF) is created for transferring data packets on a packet data channel. The TBF is a physical connection used by two mutually communicating Radio Resource (RR) peer entities to support the unidirectional transfer of PDCP Packet Data Units (PDU) from upper PDCP layers on physical channels for packet data. We will consider separately uplink TBFs (transfer of data from the mobile station to the base station) and downlink TBFs (transfer of data from the base station to the mobile station).
During an uplink TBF the mobile station will organise the data to be transferred into Protocol Data Units or PDUs. These are in turn divided into smaller parts which are distributed into data blocks on the RLC layer which defines the procedures related to information transfer over the radio interface. Each RLC data block will have a corresponding identification number as well as a multitude of associated fields containing information that relates to the contents and significance of the RLC data block. During a downlink TBF a similar arrangement of successive RLC data blocks is produced by the network and transmitted to the mobile station.
The TBF is thus established using a determined set of parameters for the data transfer, such as acknowledged/unacknowledged RLC mode, radio priority etc. If the mobile station with an existing TBF needs to transfer upper layer (or PDCP) PDUs with a different RLC mode the existing TBF is released and the new TBF is established for the new RLC mode. This means that the mobile station must request a completely new allocation of radio resources by first transmitting a request message on an access channel (PRACH or RACH; Packet Random Access Channel or Random Access Channel depending on whether or not the first one of these is available). The network will either grant or reject the request by sending a corresponding message on an access grant channel (PAGCH or AGCH; Packet Access Grant Channel or Access Grant Channel, same considerations of availability apply).
In downlink, to change RLC modes the network must allow for the termination timer in the mobile station to expire for terminating the existing TBF allocation, and establish a completely new TBF by sending a Packet Downlink Assignment message on a PCCCH or CCCH (Packet Common Control Channel or Common Control Channel depending on availability).
In the prior art systems it has not been possible to transfer simultaneously PDCP PDUs using different RLC modes, different radio priorities or different throughput classes. This is a difficult limitation, because in a GPRS system a mobile station may support different types of services and therefore there may also exist a need to transfer PDCP PDUs with different parameters simultaneously. Especially, if one of the supported services is a real time service, the delay caused by releasing the existing TBF and the establishment of new TBF to support the service could be unacceptable.
Higher bit rates are one of the most important targets in the standardisation of new packet data services. The flexibility of services and the simplicity of the terminals are other important objectives. In order to achieve higher bit rates the terminals may use several timeslots. This multi slot capability means that the mobile station is able to transmit more than one channel and/or receive more than one channel within the TDMA frame. Most service scenarios are asymmetric in nature and traffic in downlink is usually seen to be higher than in the uplink direction. Therefore traffic scenarios like 3+1 are introduced meaning that 3 timeslots are used in downlink direction and one timeslot is used in uplink direction. Current GPRS specification supports at most one connection TBF (Temporary Block Flow)) in each direction (Uplink, Downlink) regardless how many timeslots are allocated. However, in document WO 00/54464 [2] there is disclosed a method, wherein at least two TBFs can be used in one data transfer direction.
The connection is identified with the same identifier in every TDMA timeslot PDCH (Packet Data CHannel) used for the connection. This identifier is called TFI (Temporary Flow Identifier) in GPRS. This TFI is unique on all PDCH's used for the TBF. In the future when packet data services are widely used, having at most one connection per direction is an unnecessary limitation and therefore several simultaneuous connections in the same direction will be supported which are identified using different or same temporary block flow identifiers (TFI). This is commonly referred to as multiple TBFs. However these scenarios have not addressed any applicable solution for how control signalling is done assuming the multislot classes specified at the present.
In the following PACCH (Packet Associated Control CHannel) occurence when a TBF is established is described, depending on the different allocation mechanisms for the data in uplink direction, [1]. In this text, PACCH/U means uplink part of a PACCH, PDCH/D means downlink PDCH and PDCH/U means uplink PDCH.
In case of downlink TBF only, the RRBP field is used to reserve PACCH/U. The RRBP value specifies a single uplink block in which the mobile station shall transmit either a PACKET CONTROL ACKNOWLEDGEMENT message or a PACCH block to the network. When received a given DL PDCH, the RRBP refers to the same uplink PDCH.
Dynamic Allocation
The mobile station shall attempt to decode every downlink RLC/MAC block on all assigned PDCHs. Whenever the mobile station receives an RLC/MAC block containing an RLC/MAC control block, the mobile station shall attempt to interpret the message contained therein. If the message addresses the mobile station, the mobile station shall act on the message.
Whenever the mobile station detects an assigned USF value on any assigned PDCH, the mobile station may transmit a PACCH block on the same PDCH in the next block period. The mobile station shall not transmit an RLC data block in any uplink radio block allocated via the polling mechanism.
Extended Dynamic Allocation
The mobile station shall attempt to decode every downlink RLC/MAC block on all monitored PDCHs. Whenever the mobile station receives an RLC/MAC block containing an RLC/MAC control block, the mobile station shall attempt to interpret the message contained therein. If the message addresses the mobile station, the mobile station shall act on the message.
The network shall transmit all PACCH messages on the PDCH carried on the lowest numbered timeslot in the allocation.
Whenever the mobile station detects an assigned USF value on any assigned PDCH, the mobile station may transmit a PACCH block on the same PDCH in the next block period. The mobile station shall not transmit an RLC data block in any uplink radio block allocated via the polling mechanism.
Fixed Allocation Uplink
A multislot class type 1 mobile station shall monitor a radio block on an assigned PDCH for downlink a PACCH block, according to its multislot capabilities:                if the radio block is not assigned as part of a measurement gap; and        the uplink is not allocated during the radio block; and            the uplink of the TID, timeslot(s) immediately after the radio block is not allocated [3]; and    if the mobile, is multislot class 1 through 12, the uplink of the Tra timeslot(s) immediately before the radio block is not allocated, [3].    if the mobile is multislot class 19 through 29, the uplink of the Trb timeslot(s) immediately before the radio block is not allocated, [3].
The network shall leave such sets of gaps in the uplink fixed allocation for the purpose of transmission of the downlink PACCH.
A mobile station shall monitor one PDCH in the allocation for downlink PACCH except during the measurement gap. The network shall indicate that PDCH on uplink resource assignment (DOWNLINK_CONTROL_TIMESLOT parameter) according to MS multi slot class. DOWNLINK_CONTROL_TIMESLOT parameter shall always indicate a timeslot number, which is used for TBF uplink.
A Multi slot Class type 2 mobile station shall monitor all assigned PDCHs for PACCH, unless the mobile station also has current downlink TBF, in which case PDCH assigned for the downlink TBF shall take precedence.
After the fixed allocation is exhausted, the mobile station shall continue to monitor all assigned PDCH(s) that it is able to monitor according to its multi slot class.
In the case of simultaneous uplink and downlink TBFs, the mobile station shall monitor all assigned downlink PDCHs and any uplink PDCHs it is able to monitor.
The mobile station may transmit a PACCH block on any uplink radio block allocated via the ALLOCATION_BITMAP.
In the case of simultaneous uplink and downlink TBFs, the mobile station shall not transmit an RLC data block, in any uplink radio block allocated via the polling mechanism [1] (subclause 10.4.4).
The problem of uplink controlling is next described in more detail referring to FIG. 3. FIG. 3 shows a downlink TDMA frame 301 and an uplink TDMA frame 302, which both have 8 time slots TN0 . . . TN7. FIG. 3 depicts a multi slot, class 4 MS i.e. 3 time slots in downlink and 1 time slot in uplink. There are two parallel connections active in the downlink data transfer using uplink time slots TN1, TN2 and TN3, 310. The temporary block flow TBF-A is transferred on time slots TN1 and TN2, and a temporary block flow TBF-B is transferred on the time slot TN3. In the uplink direction there is one connection TBF-U, which is allocated on uplink TN2, 322. If the connections use acknowledged model RLC then RLC blocks from all the TBFs have to be acknowledged on the same uplink channel PACCH/U (Packet Assosciated Control CHannel/Uplink) on time slot 322, due to the multislot class constraints.
An uplink control channel is used, for example, for transferring acknowledgement messages, which inform whether the downlink data transfer of a determined TBF has been successful. Packet downlink ack/nack message has an information element “Global TFI” that identifies the temporary block flow to which acknowledgement is related. If the network has allocated the same TFI values for two connections, e.g. TFI-A and TFI-B have the same value, then downlink TBF cannot be unambiguously identified in Packet downlink ack/nack message. RRBP (Relative Reserved Block Period) cannot be used as such for TBFs, because e.g. in the previous example, it could reserve blocks on TN1 or TN3, which would not be allowed.